The question, of course, refers to George Costanza, the clueless sidekick of “Seinfeld” fame who carried a wallet so filled to capacity that it finally exploded. In recent years, the big players in the payment industry — merchants, banks, mobile-phone companies — have touted a day when such an overstuffed leather carry-all will become as much a relic as the typewriter or LP.

But even with a new wave of retail giants, including Wal-Mart and Target, entering the digital-wallet space, consumers may still have rightful reason to be skeptical — at least for another year or two — and to hold on to their plastic, say experts who track mobile commerce.

For starters, the problem is one too many competing technologies. In addition to the newly announced Merchants Customers Exchange, the other big names in mobile payments include Google and Isis. A wide-open field poses a dilemma for consumers, since nobody wants to get stuck with the mobile-wallet version of Betamax.

On top of that, the individual payment systems are still going through an extensive period of refinement. When Google Wallet first launched, for example, it worked only with a Citibank-issued card. Just this past month, Google announced it finally expanded to support “all credit and debit cards from Visa, MasterCard, American Express and Discover.”

But limitations of one sort or another still exist with most of the major mobile-payment services — and will continue to do so for a while. For example, not all smartphones work with all services. “It’s just the market shakeout,” says Hank Israel, a partner with Novantas, a prominent management consulting firm.

On top of that, there’s a broader question of whether using a mobile payment system, which requires its own version of “swiping,” is any easier or more convenient than taking out that piece of plastic.

For example, consumers still need to carry a physical form of identification (the mobile driver’s license doesn’t appear to be in our near future). And they still need to carry some cash, since the occasional merchant insists upon it (ever try paying a babysitter with a digital wallet?).

Most important, while mobile commerce is gaining ground — transactions are expected to grow from $172 billion in 2012 to $600 billion in 2016, according to Gartner Inc. — thousands of merchants are still not equipped to accept mobile payments, making it harder for consumers to leave the credit cards at home.

Plus, the leather wallet has one distinct advantage: It doesn’t require a battery. Even a digital-wallet fanatic is “always going to want some kind of backup,” says Daryl Colwell, a vice president at MediaWhiz, a digital media agency.

If there’s good news for consumers, however, it’s that as retailers embrace mobile commerce they could be offering deals of all sorts as part of the formula, experts say. Think “instant” coupons or other offers, designed to trigger a last-minute purchase.

And just as retailers will offer shoppers a special one-time discount for signing up for an in-house credit card, they could do the same with a mobile-wallet platform.

Mr. Colwell believes it’s this sort of promotion that could ultimately make the mobile wallet a mainstream consumer reality. “As long as there’s a big incentive for shoppers to jump on board, they’re going to jump on board,” he says.